AC3 Audio Playback Through Regular TV

Maybe I just don’t understand the audio settings available to me. Help!

Case:

I have a x264 file with ATSC (AC3) 5.1 Audio track. When I play a movie with its audio through HDMI to a regular HD TV it is a garbled mess. If I route the audio through the AC3 equipped sound system (using my optical audio cable), no problems. This occurs with all AC3 files I have tried (dozens). It’s a problem with the ATV2 in the other room plugged into a cheap-ass smallish bedroom HD TV.

Question:

Is there a setting in either mediaplayer/infuse or somewhere in the factory appletv2 settings to mixdown the AC3 5.1 Audio to stereo in real time?

I think I have seen reports that the setting that fixes this problem is Infuse Settings → Playback ->. DTS Audio → Disable